The fundamental physical principle of electrocoat is that materials with opposite electrical charges attract each other. An electrocoat system applies a DC charge to a conductive substrate immersed in a bath of oppositely charged paint particles. In theory, the paint particles are drawn to the conductive substrate and paint is deposited on the conductive substrate, forming an even, continuous film over every surface, in every crevice and corner, until the electrocoat reaches the desired thickness. At that thickness, the film insulates the conductive substrate, so attraction stops and the electrocoat process is complete. The desired thickness can be controlled by manipulating the temperature of the bath, the amount of voltage applied, and/or by the coating deposition time. Depending on the polarity of the charge, electrocoat is classified as either anodic or cathodic.
While the theory of electrocoat suggests that each and every surface of a conductive substrate immersed in the bath reaches the same film thickness, this is not always the case. In fact, it is ordinarily very difficult to electrocoat recessed areas of conductive substrates, especially interior regions of hollowed out conductive substrates.
For example, it is very difficult to coat the internal surfaces of hand grenade bodies. Grenade bodies have a nearly spherical shape with only a small hole to access its internal surfaces. Thus, these interior surfaces typically have limited internal paint coverage due to their part geometry.
It would thus be highly desirable to provide a mechanism to attain greater internal paint coverage for grenade bodies. This in turn can be translated to other conductive substrates having similarly difficult to paint internal geometries.
Another related issue with electrocoated films in general relates to the issue of electrode contact points on the surface of the coated conductive substrate and their effect on film quality and corrosion protection. Generally speaking, the coated films in the areas of the contact points may have varying film thicknesses, and thus may be more prone to corrosion and/or provide an unpleasing appearance.
Thus, it would be highly desirable to locate these electrode contact points in recessed or hidden areas that are less likely to be exposed to the environment and to provide a pleasing outer appearance. In the context of a hand grenade, such an area would be along an internal surface that is not exposed to the environment during subsequent use.